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Fisheries Management. Renewable and Nonrenewable Resources Maximum Sustainable Yield A. Schaefer Model B. Beverton-Holt Model Resource Limited Population Practical and Theoretical Problems. Renewable and Nonrenewable Resources. Geological Resources are Nonrenewable Biological Resources - PowerPoint PPT Presentation
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Fisheries Management
I. Renewable and Nonrenewable Resources
II. Maximum Sustainable Yield
A. Schaefer Model
B. Beverton-Holt Model
III.Resource Limited Population
IV.Practical and Theoretical Problems
Renewable and Nonrenewable Resources
I. Geological Resources are Nonrenewable
II. Biological Resources
A. If managed properly, they can be Renewable
B. If managed improperly, they become Nonrenewable
Maximum Sustainable Yield
I. Schaefer ModelRelates Fish Catch to Fishing Effort
II. Beverton-Holt ModelRelates Fish Catch to Fish
Population Dynamics
“It took fisheries scientists until the 1930s to prove scientifically that the Victorian scientist T.S. Huxley had been incorrect whenhe said that the great sea fishes were inexhaustible and that itwas futile to try to regulate the great fisheries.”
1. You do not PROVE something scientifically.
2. In hindsight, Huxley could have done better. By the Victorian Era, the Right and Grey Whales had already been wiped out in the North Atlantic.
3. In any case, by mid-century, some people realized that a science-based management of fisheries was necessary.
Maximum Sustainable Yield:Assumptions Used in its Development
I. Oceanic Ecosystems are Infinitely Resilient
II. It Will be Possible to Accurately Determine Critical Parameters of Fish Populations
III. If a Fish Stock is Overharvested, Fishing Pressure Will Be Reduced
Maximum Sustainable Yield:Political Context Within Which it Developed
I. Post-War American Domination of the Seas
II. Economic Activities Don’t Require Regulation
Maximum Sustainable Yield
I. Schaefer ModelRelates Fish Catch to Fishing Effort
II. Beverton-Holt ModelRelates Fish Catch to Fish
Population Dynamics
Beverton-Holt Model: Application to a Resource-Limited Population
F
Mortality declines with fishing because:
1. Caught fish don’t die a natural death;
2. A fished population is a younger population, with a lower death rate;
3. Individuals in a fished population have access to more resources, so they are healthier and have a lower death rate.
Beverton-Holt Model: Application to a Resource-Limited Population
F
Gross Production declines with fishing less rapidly than M declines because:
1. Individuals in a fished population have access to more resources, so they grow faster and have higher fecundity.
Practical and Theoretical Problems
I. Practical Problems
Determination of Population Parameters(Beverton-Holt Model)
Determination of Fishing Effort(Schaeffer Model)
OTOLITHS: Information that can be obtained from the
analysis of otolith biomineralization patterns
Age
OTOLITHS: Information that can be obtained from the
analysis of otolith biomineralization patterns
Spawn Date
Hatch Date
Metamorphosis
Growth History
Age
For Those Who May Be Interested:
More information on otoliths can be found at
http://www.marinebiodiversity.ca/otolith/english/daily.html
Population Size: Estimate by Tagging
18,055 herring tagged and released
Subsequent to release, 810,000 fish surveyed
13 tags recovered
(13/810,000) = (18,055/1.12x109)
Population size estimated at 1.12x109 herring
Determination of Fishing Effort
I. Units used to measure effort must be defined
II. Type of fish-finding technology andfish-harvesting technology must be taken into account
III. “I fish, therefore I lie” must be factored in
Theoretical Problems
Variable Recruitment
K and r Selection
Stock Stability
Effects of Competitors
Recruitment - Reproduction Time Lag
Percentage contribution of year classes of Norwegian spring spawn herring to the adult stock from 1954 through 1962. The very good year class of 1950 began first appearing in significant numbers in 1954 and dominated the adult stock throughout this period.
Mathematical Modeling of Population Dynamics:
The Logistic Equation
and
r-selected and K-selected populations
rate of change = ⎟⎠⎞⎜⎝
⎛ −KN1rN
The Logistic Equation
N = Population Size
R = Reproductive Capacity of the Species
K = Carrying Capacity of the Ecosystem
Multiple “Steady States” Possible with the Logistic Equation
Pierre Francois Verhulst:Limited Growth
Multiple “Steady States” Possible with the Logistic Equation
Table 4.2. Characteristics of r-selected and K-selected populations
parameter r-selected K-selected
Environment variable and/or unpredictable
constant and/or predictable
Lifespan short long
Growth rate fast slow
Fecundity high low
Natural mortality high low
Population dynamics unstable stable
Table 4.3. Example of effect of natural mortality and growth on yield of a year class
Age Number of individuals Weight per individual Yield per recruit
3 1,000,000 15 15.0004 900,000 17 15.3005 810,000 19 15.3906 729,000 21 15.3097 656,100 23 15.0908 590,490 25 14.762
MAXIMIZING YIELD PER RECRUIT CLASS
How to Deal with Catch Variability
The Canadian Cod Example:
Fished to Commercial Extinction BeforeEstablishment of a Moratorium: No Recoveryof the Stock, No Recovery of the Fishery
The Norwegian Cod Example:
Moratorium Established in Response toDeclining Catch: Stock Recovered, as dida Viable Fishery
HOW MANY FISH SHOULD WE CATCH?
Given the uncertainties involved in estimatingthe maximum sustainable yield; and
Given that the economics of attaining the maximumSustainable yield don’t make sense; and
Given that harvesting the maximum sustainable yieldmakes the population especially prone to collapse;
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